Torrential rainfall from thunderstorms could create flash flooding issues in parts of East Tennessee this weekend, according to the National Weather Service.
The NWS’s Morristown weather forecast office on Thursday issued a Flood Watch for all of East Tennessee, including Scott County, from 12 p.m. Friday through 8 p.m. Sunday, amid rising confidence that widespread thunderstorms will develop at least Friday and Saturday.
In the Flood Watch, the NWS said that “excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations.” The agency said that areas at risk will be any that receive multiple rounds of heavy rainfall, with the greatest threat being Friday night through Saturday.
The NWS has a 90% chance of thunderstorms in the forecast for the Oneida area Friday, Friday night, and Saturday.
An atmospheric trough is expected to develop over the eastern United States on Friday, with multiple rounds of energy rotating the base of the trough to provide fuel to an air mass that is expected to become increasingly moist with an influx of moisture from the Gulf. The NWS said Thursday that precipitable water values in the atmosphere over Tennessee will be in the 90th percentile for this time of year — meaning the air will be more moist than it is roughly 90% of the time in mid July.
In a forecast discussion posted Thursday afternoon, NWS-Morristown said that it expects a “semi-organized” cluster of thunderstorms to impact the region early Friday afternoon, some of which could be strong to severe. After a lull in the thunderstorm activity by late afternoon, the NWS expects widespread thunderstorms Friday night into Saturday. It is during this timeframe, the agency said, that training of thunderstorm cells could lead to flooding potential.
Short-range models Thursday afternoon showed limited precipitation over the northern Cumberland Plateau region from Friday through lunchtime Saturday. However, diurnal thunderstorms are notoriously hard to predict more than a few hours in advance. Among global models, the American GFS model suggested the bullseye for rainfall potential during the weekend would be over the northern plateau, with as much as half a foot of rain possible through the end of the day Sunday. However, the same shortcomings hold true with global models: it is very difficult to nail down specifics of convective thunderstorms more than a few hours in advance.
Relatively high chances of thunderstorms are expected to continue into Monday before drier weather returns to the forecast. Temperatures are expected to be slightly below normal for this time of year, due to the cloud cover and potential rainfall.
Although the northern plateau region officially remains in a drought, rainfall amounts have ticked up sharply since the start of summer. Since June 18, more than 8.2 inches of rain have been recorded in Oneida, which is more than double the amount that can typically be expected during that time frame.
